The present invention relates to wire cutting electric discharge machines, and especially to a method and apparatus for vertically calibrating a wire of a wire cutting electric discharge machine and measuring heights of an upper holding guide and a lower holding guide.
A conventional device for vertically calibrating a wire of a cutting electric discharge machine is illustrated in FIG. 1. This vertical calibration device 1 has an upper calibration board 2 with a surface PX1 being coplanar with a surface PX2 of a lower calibration board 3, while a surface PY1 of the upper calibration board 2 is coplanar with a surface PY2 of the lower calibration board 3. The upper calibration board 2 and lower calibration board 3 are insulatively fixed to a main body 7. The surfaces PX1 and PX2 are respectively perpendicular to the surfaces PY1 and PY2, and these surfaces are all perpendicular to the bottom of the main body 7 and a horizontal base table (not shown). For performing vertical calibration, it is necessary to install the vertical calibration device 1 on the base table to make the surfaces PX1 and the surface PX2 parallel to the X axis, while making the surfaces PY1 and PY2 parallel to a Y axis. A driving machine (not shown) is used to drive a (copper) wire under tension. Contact points on the surfaces PX1 and PX2 are first derived in X and U directions at the same time, and then contact points on the surfaces PY1 and PY2 are acquired in Y and V directions. Thereby, the position of a vertical line is obtained.
A method for measuring heights of an upper holding guide and a lower holding guide of a wire cutting electric discharge machine through the use of the conventional vertical calibration device 1 is illustrated in FIG. 2. As shown in FIG. 2, a wire 4 is disposed at a position corresponding to the above-obtained vertical line. To obtain a distance x from a base table (not shown) to the upper holding guide 5 and a distance y from the base table to the lower holding guide 6, at first, the upper holding guide 5 is displaced away from the position of the vertical calibration device 1 along the X and U directions by a distance e, indicated by a tilt wire 4xe2x80x2 shown in FIG. 2. Then, the upper holding guide 5 and lower holding guide 6 move with a constant speed toward the vertical calibration device 1 to allow this tilt wire 4xe2x80x2 to move for a distance d and reach the position of a tilt wire 4xe2x80x2 in contact with the lower calibration board 3 of the vertical calibration device 1. After the upper holding guide 5, and lower holding guide 6, and wire 4 return to the vertical position, the above procedures are repeated to move the lower holding guide 6 away from the vertical calibration device 1 by a distance and use a tilt wire to find a contact point with the upper holding guide 2 of the vertical calibration device 1, as indicated by a tilt wire 4xe2x80x2xe2x80x3 shown in FIG. 2, by which a distance c of movement is obtained. From the triangular relation of FIG. 2, we may derive:
X=[a(cxe2x88x92e)+b(exe2x88x92d)]/(cxe2x88x92d)xe2x80x83xe2x80x83(1)
Y=(bdxe2x88x92ac)/(cxe2x88x92d),xe2x80x83xe2x80x83(2)
where a, b, and c are known, and c and d are respectively the distances by which the tilt wires shift to contact the upper calibration board 2 and the lower calibration board 3. Thereby, the distances x and y, respectively, from the upper holding guide 5 to the base table and from the lower holding guide 6 to the table are obtained.
However, the above conventional device and method for vertically calibrating a wire of a wire cutting electric discharge machine have the following disadvantages.
The vertical calibration device 1 is required to be mounted parallel to the base table, or otherwise multiple calibrations in the X and Y directions for converging to a vertical position must be performed. However, the parallel arrangement with the table for the calibration device is difficult to implement, and inaccuracy of the vertical position would adversely affect the determination of positions of the upper holding guide and lower holding guide.
When estimating the positions of the upper holding guide 5 and lower holding guide 6, equations (1) and (2) include two variables c and d which are difficult to measure and may enlarge the errors in calculating x and y. To overcome the problems mentioned above, a method and apparatus for a circular type of vertical calibration have developed.
Accordingly, the primary object of the present invention is to provide an apparatus and a method for vertically calibrating a wire of a wire cutting electric discharge machine, wherein upper and lower coaxial circles of different diameters are used for parallel arrangement of the apparatus with a base table, so as to increase speed and accuracy of measurement performed by the apparatus and method
Another object of the present invention is to provide an apparatus and a method for vertically calibrating a wire of a wire cutting electric discharge machine, wherein upper and lower coaxial circles of different diameters are used, whose cone angle is used for calculation of heights of an upper holding guide and a lower holding guide.
A further object of the present invention is to provide an apparatus and a method for vertically calibrating a wire of a wire cutting electric discharge machine, wherein contact between a copper wire and a calibrator is reduced to prevent damage to the copper wire, so as not to affect the accuracy in calibration.
To achieve above objects, the present invention provides an apparatus for vertically calibrating a wire of a wire cutting electric discharge machine, which includes: a main body having a flat bottom, and an upper calibration board and a lower calibration board insulated from and connected to one lateral surface of the main body. The upper calibration board is formed with an upper circle and the lower calibration board is formed with a lower circle, wherein the upper circle and lower circle have different diameters but are coaxial. The vertical calibration apparatus of the present invention is coordinated with a machine controller to detect whether the wire is in contact with the circles. First, the calibration device is mounted on a base table. Since the upper circle and lower circle are coaxial circles, it is unnecessary to consider the direction of the apparatus. The wire, under tension, passes through the circles, and then, the wire is moved to contact the upper circle and lower circle to determine the centers of the upper circle and lower circles and therefore the calibration is accomplished. Thereby the present invention improves measuring accuracy and speed.
After calibration, since the height of the lower circle, the height of the upper circle, the radius of the upper circle, the radius of the lower circle, and a cone angle of the two circles are all known in advance, the equation for acquiring the height of an upper holding guide contains only one variable, which is the translated distance of the wire in tension from the vertical position to the circle edge. The equation of the height of a lower holding guide also contains one variable similarly estimated as the upper one. The prior art formula for deriving the height of the upper or lower holding guide has two variables. The formula of the present invention has only one variable required to obtain the height of the upper or lower holding guide. Therefore, in the present invention, the heights of the upper holding guide and lower holding guide can be more easily and accurately obtained than the prior art.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawings.